The present invention relates to sputtering targets and sputtering target assemblies as well as methods of making the same. The present invention also relates to a bonding method for making a sputtering target assembly, preferably at a low temperature.
In the sputter application field, typically a sputtering target assembly has a sputtering target and a backing plate. For instance, a metal target or metal target blank (e.g., tantalum, titanium, aluminum, copper, cobalt, tungsten, etc.) is bonded onto a backing plate, such as a backing plate flange assembly such as copper, aluminum, or alloys thereof. To achieve good thermal and electrical contact between the target and the backing plate, these members are commonly attached to each other by means of soldering, brazing, diffusion bonding, clamping, and by epoxy cement and the like. However, sputtering target assemblies bonded by methods at high temperatures can warp the assembly during use which affects performance of the sputtering target assembly, especially when a large difference exists between the coefficients of thermal expansion for the target and the backing plate. Moreover, the differential thermal expansion between the target material and the backing plate material which occurs when bonding is accomplished at elevated temperatures by soldering, brazing, or diffusion bonding, generates very high levels of mechanical stress in the metal bodies. The mechanical stress often causes deflection of the target assembly and can cause the bond to fail so that the target separates from the backing plate.
The bonding process also adds weight and creates the risk of having a target assembly debond while in use. The debonding risk is even more possible due to the continuing progression of the industry to use larger and larger targets.
Additionally, the high temperatures associated with some conventional bonding methods can result in undesirable grain growth in the target metal.